The invention relates to a tomographic apparatus for producing transverse layer images of a radiography subject, with a patient couch, with a radiation measuring arrangement comprising a radiation source producing a fan-shaped beam of rays which penetrates the radiography subject and whose cross sectional extent perpendicular to the layer plane is equal to the layer thickness and the beam transverse extent being of such a magnitude in the layer plane that the whole radiography subject is penetrated, and a radiation receiver consisting of a row of detector elements, which detects the radiation intensity behind the subject, with a rotating device for the measuring arrangement and with a computer for the transformation of the signals supplied by the radiation receiver into a tomographic layer image.
A tomographic apparatus of this kind is described for example in the German Offenlengungsschrift 25 53 187. In this type of tomographic apparatus the scanning of a patient is carried out by rotating the measuring arrangement through an angle of, for example, 360.degree.. During this rotation the radiation receiver can be periodically interrogated at equal intervals of time. The number of measured values per scanning process is therefore given by the number of the interrogation processes of the radiation receiver; i.e., by the number of the projections and the number of detector elements in the radiation receiver.
In order to achieve a good image quality it is necessary, on the one hand, to select a sufficiently high number of projections, but on the other hand also to provide a sufficiently high number of detector elements in the radiation receiver. It is not possible however for the number of detector elements in the radiation receiver to be increased indefinitely.